Cancer and infectious disease are significant health problems throughout the world. Although advances have been made in detection and therapy of these diseases, no vaccine or other universally successful method for prevention or treatment is currently available. Current therapies, which are generally based on a combination of chemotherapy or surgery and radiation, continue to prove inadequate in many patients.
Cancer is the result of cumulative multiple genetic mutations, which result in the activation of oncogenes and/or the inactivation of tumor suppressor genes. It is the differential expression of these critical genes and their downstream effectors that enables cells to override growth controls and undergo carcinogenesis (1, 2). The pathological changes that arise in cancer, whether caused by a single gene mutation or multiple genetic alterations, are essentially driven by changes in gene expression (1, 2). In the malignant progression of astrocytic cancers, it has been shown that accumulation of multiple genetic lesions underlies the neoplastic process. These lesions include mutations of the genes p53, p16, RB, and PTEN, as well as amplification of CDK4 and EGFR (3, 4). Although these known genetic abnormalities have been well-documented in the formation of the most malignant brain tumor, glioblastoma, recent insight into the extent of gene expression differences underlying malignancy reveals that hundreds of gene transcripts may be expressed at significantly different levels between normal and neoplastic cells (5). Therefore, there is considerable room for the identification of novel genes that are differentially expressed in brain tumor cells to further our understanding of the complex molecular basis of these neurological cancers. Furthermore, this endeavor has direct clinical relevance if combined with the development of innovative rational therapies that specifically target these differentially expressed gene products.
A variety of methods are currently employed to isolate genes associated with particular differential phenotypes. Subtractive hybridization (6), differential display (DD) (7–10), representational difference analysis (RDA) (11–14), serial analysis of gene expression (SAGE) (5, 15), and suppression subtractive hybridization (SSH) (16, 17) all allow for the cloning and identification of differentially expressed sequences. While all these techniques identify tissue-enriched mRNAs, none select for tissue-specific proteins. There remains a need for a differential screening technique that provides actual confirmation of the presence of a protein product, not just the capacity to synthesize a protein. In addition, there is a need for proteins with antigenic determinants that may be recognized by the immune system.